Boston bombings suspect Dzhokhar Tsarnaev on April 19, 2013, as he emerged from a boat stored in a Watertown, Mass., backyard. The red dot of a police sharpshooter's laser sight can be seen on his forehead. Mass. State Police Sgt. Sean Murphy/Boston Magazine hide caption

itoggle caption Mass. State Police Sgt. Sean Murphy/Boston Magazine

Blue and yellow are the colors for tributes to victims of the Boston Marathon. Street lights on the route of this year's race are among the places they're showing up. Andrew Burton/Getty Images hide caption

itoggle caption Andrew Burton/Getty Images

Carol Downing is still haunted by memories of last year's marathon. But she's excited about reuniting with other survivors. Michael Dwyer/AP hide caption

itoggle caption Michael Dwyer/AP

Boston Red Sox's Jonny Gomes places the championship trophy and a Red Sox baseball jersey at the Boston Marathon Finish Line during a pause in their World Series victory rolling rally in Boston on Saturday. Elise Amendola/AP hide caption

itoggle caption Elise Amendola/AP

Tamerlan Tsarnaev, as seen in a video taken on April 15 near the finish line of the Boston Marathon. FBI.gov hide caption

itoggle caption FBI.gov

Boston Police Commissioner Edward Davis talks with reporters during the hunt for the Boston Marathon bombers in April. Michael Reynolds /EPA/Landov hide caption

itoggle caption Michael Reynolds /EPA/Landov

Boston bombings suspect Dzhokhar Tsarnaev on April 19 as he emerged from a boat stored in a Watertown, Mass., backyard. The red dot of a police sharpshooter's laser sight can be seen on his forehead. Mass. State Police Sgt. Sean Murphy/Boston Magazine hide caption

itoggle caption Mass. State Police Sgt. Sean Murphy/Boston Magazine

Marine Sgt. Maj. Damion Jacobs (left) and Marine Capt. Cam West visit with Boston emergency workers who responded to the bombings at the Boston Marathon. Oren Dorell for USA Today hide caption

itoggle caption Oren Dorell for USA Today

Celeste Corcoran is transported to Spaulding Rehabilitation Hospital on April 28. Ellen Webber for NPR hide caption

itoggle caption Ellen Webber for NPR

Celeste Corcoran and her daughter, Sydney, were injured in the Boston Marathon bombings. Ellen Webber for NPR hide caption

itoggle caption Ellen Webber for NPR